Electrocardiograms (ECG) are electrical signals representing the impulses generated by the heart. The ECG signal and waveform is characterized by the P, QRS, and T waves, as seen in FIG. 1, produced during the atrial and ventricular contraction and relaxation of the heart muscle. FIG. 1 illustrates an example of a typical ECG signal 10, relatively free of any corruption or noise. ECG signal 10 demonstrates the characteristic P wave 12, Q wave 14, R wave 16, S wave 18, and T wave 20 features. ECG signals can be acquired using electrodes mounted to the skin of the subject in an area external to the heart. These electrodes can be affixed to the skin using adhesive on one surface of the electrodes. The electrodes can then acquire a signal from the electrical activity in and around the heart. The terms “ECG signal” and “signal” can refer to the analog output of ECG electrodes, as well as a processed or unprocessed sampled data points, e.g., sampled data points produced using an A/D converter. The analog signal and/or sampled data points may be filtered. The signal can then be further processed, stored, and/or transmitted or routed to a device configured to display the signal.
Artifacts, which include powerline interference, motion artifacts and electromyogram (EMG) signals, corrupt the ECG signal with “noise” and affect the performance of feature detection algorithms. It also affects accurate diagnosis by clinicians. Motion and EMG artifacts are frequent occurrences due to the movement of the test subject and electrical activity of other muscles near the heart. Corrupted ECG signals (e.g., ECG signals with motion and EMG artifacts) can be seen in FIGS. 2 and 3. Long period noise in a corrupted ECG signal, most notable in FIG. 2, is typically caused by subject motion and is referred to as a motion artifact. Higher frequency distortion shown in both FIGS. 2 and 3 in the corrupted ECG signal can be caused by the electrical activity of muscles surrounding or near to the heart. This type of distortion is referred to as EMG artifacts.